In the 80s, Vault Corporation introduced various products in the Prolok family like HDPROLOK and CHRONOLOK, but most of these remained references in ads. They also created a dongle named ROMLOK and later released the disk duplication machine ProLoader. The Prolok Software Protection Disk is a fascinating piece of history, with unique fingerprints on each disk creating three bad sectors. PROLOK.EXE was late in Prolok’s life and was heavily obfuscated to protect software. Despite its complexities, Prolok could be bypassed, leading to a lawsuit with Quaid Software. Unfortunately, Vault Corporation made a damaging business decision with Prolok Plus that caused reputational harm and eventually led to their decline. Robert McQuaid of Quaid Software was interviewed about the court battle. The history of Prolok and attempts to emulate it for preservation are detailed, highlighting the technical aspects of weak bits in disk images and the emulation challenges faced.
https://martypc.blogspot.com/2024/09/pc-floppy-copy-protection-vault-prolok.html